Spatial distribution of phytochromes.

Phytochromes are chromoproteins which mediate several light responses in plants. Phytochrome proteins are encoded by a gene family which is currently being characterized in several plant species. Analysis of type-specific mutants of two well-characterized members of the family, PhyA and PhyB, indicates that these proteins have distinct functions. Much remains to be learned about the mechanisms by which the phytochromes carry out their distinct and diverse functions. It is hoped that information concerning the localization of phytochromes, at the whole plant and subcellular levels, will aid in elucidating the mechanism of phytochrome function. This review, which summarizes information about phytochrome distribution, has an emphasis on recent reports in which the molecular species of phytochrome are differentiated. However, classical data are also included and reinterpreted using knowledge of the phytochrome family.